US SPEC and the American Segmental Bridge Association

US SPEC is pleased to announce we have joined the American Segmental Bridge Institute (ASBI) as a Materials Supplier. ASBI is a nonprofit organization that provides a forum where owners, designers, constructors, and suppliers can meet to further refine current design, construction and construction management procedures, and evolve new techniques that will advance the quality and use of concrete segmental bridges.

ASBI is a focal point for the development of technical information for design and construction of segmental concrete bridges in the U.S. and countries around the world. Segmental bridges are now a multi-billion dollar market in the U.S. with ASBI providing educational programs and publications in response to industry needs.

Technical Director Bryan Smith says our membership in ASBI is “not solely to show our support for the bridge construction industry, but also to work in community with our customers. Joining ASBI is exciting for us because it offers an opportunity to be a part of a larger community with shared interests. It allow us to learn and become better at what we do best - serve our customers with a quality foot forward.”

Additionally, as of May 2012, two of our team members will have completed the ASBI Grouting Certification Program.

Freeze Thaw and ASTM C-672

Durability is the ability of concrete to resist weathering action, chemical attack and abrasion while maintaining its desired engineering properties. How durable concrete products need to be depends on the kind of environment they will be exposed to. As cold weather approaches, concepts like freeze-thaw and resistance to deicing salts become important to understand. When water freezes, it expands 9%. As the water in moist concrete freezes, it produces pressure in the pores of concrete. If this pressure exceeds the tensile strength, the cavity will dilate and rupture. Successive freeze-thaw cycles will then eventually cause expansion and cracking, scaling, and/or crumbling of the concrete. Deicing chemicals, used for snow and ice removal, can aggravate freeze-thaw deterioration. Therefore, when using cement products, such as patching materials, on concrete roadways it is important that these materials have a strong resistance to the effects of these harsh conditions and chemicals.

ASTM C-672 is the standard test method for Scaling Resistance of Concrete Surface Exposed to Deicing Chemicals. It covers the determination of the resistance to scaling (local flaking or peeling of a finished concrete surface) of a horizontal concrete surface exposed to freeze-thaw cycles in the presence of deicing chemicals. The test is intended for use in evaluating this surface resistance qualitatively by visual examination.

How is the test performed? Specimens are placed in a solution of calcium chloride and water with a concentration that imitates deicing salts; they are then placed alternatively in a freezing environment and a room temperature environment. This cycle is repeated daily and the surface is flushed off thoroughly at the end of every 5 cycles to visually examine the surface. Generally, 50 cycles is sufficient to evaluate the surface and the condition of the surface is reported using a rating scale from 0 to 5; meaning there is no scaling present and 5 indicating there is severe scaling (coarse aggregate is visible over the entire surface). Quality patching products, like US SPEC Transpatch, should be displaying scaling resistance after this 50 cycle test.

Cold Weather: Installation of Epoxies

Procedural adjustments should be made when setting and grouting epoxies during periods of cold temperatures. Cold epoxy liquids, along with air and surface temperatures, can cause workability problems and slow the curing process. Observe the following recommendations for best results:

• Keep epoxy liquids stored at room temperature (70 degrees) for 12 to 24 hours before use. Cold liquids can be warmed by placing unopened containers in warm water.
• Epoxy liquids are freeze/thaw stable. Frozen liquids can be thawed at room temperature or by placing in warm water.
• Cold temperature will make epoxy stiffer to work with and extend set time. Mixing, spreading, grouting, and cleanup will require additional attention if done in cooler temperatures. Completed work should be protected from foot traffic for longer periods. A floor grouted at 50 degrees should be protected at least 32 hours.
• For best results, surface temperatures should be between 60 degrees and 90 degrees.
• Consider using these products specifically designed for use in very cold weather. US SPEC Gelbond Sub-Zero is designed to gun at -15 degrees.
• Consult manufacturer's recommendation for epoxy usage when optimum conditions do not exist.

Cubes vs. Cylinders: Mold Materials and Shapes

ASTM specifies non-shrink mortars be tested in a 2"x 2" metal cube ( ASTM C-109) instead of a 4"x 8" cylinder mold (ASTM C-39). Both test method specifications are testing compressive strength, but how is it decided whether to cast a cube specimen or a cylinder specimen?

Hydraulic mortars (including non-shrink grouts) are designed for precision load transfer applications, so they are designed with expansive properties. Non-shrink grouts are typically placed in confined forms where the expansive properties are limited to an upward direction. This results in maximum effective bearing area support and stronger physical properties. As a result of the non-shrink grout being restricted from expanding freely, it has now developed into a stronger and denser material.

Testing conditions that represent the application should produce representative test data. For example, if a non-shrink grout freely expanded in a non-restrictive mold material (such as plastic), the compressive strength test data would be low and would produce a less dense finished product. This could be a factor if "value-engineering" were used.

Traditional concrete is not designed with expansive properties. Therefore, a resistive mold material is not necessary. In fact, concrete will naturally undergo some shrinkage (generally about 1%) within the first 24 hours. Consequently, plastic or disposable cylinder molds (with dimensions of the hardened specimen that comply with ASTM C-39) are the standard mold material for concrete test specimens in use today.

In his book Properties of Concrete, Adam Neville says:

It is difficult to say which type of specimen, cylinder or cube is "better", but even in countries where cubes are the standard specimen, there seems to be a tendency, at least for research purposes to use cylinders rather than cubes. Cylinders are believed to give a greater uniformity of results for nominally similar specimens because their failure is less affected by the end restraint of the specimen; their strength is less influenced by the properties of the coarse aggregate used in the mix; and the stress distribution on horizontal planes in a cylinder is more uniform than on a specimen of square cross section. (594)

He goes on to say that cylinders are cast and tested in the same direction whereas for cubes the test is transverse.

Hot Weather Concreting

With summer in full force, it is important to understand how hot weather conditions affect concrete and how to prevent these adverse effects. Once concrete has been damaged by hot weather, it can never be fully restored.

What is considered "hot weather" in regards to concreting? According to ACI 305, "Hot Weather Concreting," hot weather is any combination of the following weather conditions: high ambient temperature, low relative humidity, solar radiation and/or wind.

Common problems/concerns that arise during these conditions include:

• Increased water demand
• Accelerated slump loss
• Placing and finishing difficulties resulting from accelerated set times
• Rapid drying causing increase in plastic shrinkage cracking
• Long term strength loss
• Potential for thermal cracking in massive structures

Precautionary measures can be taken to alleviate these effects:

• Moisten subgrades and forms so water wont be absorbed from the mix
• Prior to placing, cool aggregates and mixing water to reduce initial temperatures. Use sunshades, windbreaks and temporary covers, such as moistened burlap, over the surface to keep surface temperature down and hold in moisture. Consider fogging to preserve humid conditions.
• To retain moisture, make finishing easier, minimize shrinkage cracking and reduce water demand, use an evaporation retardant such as US SPEC Monofilom ER
• Cure concrete surfaces with US SPEC Maxcure Resin Clear or Maxcure Wax White when surfaces are hard enough to resist marring.
• Seal with a good quality sealer, such as Roca Seal or BRS-25, when concrete is fully cured.

Earn LEED Points Using Concrete

The LEED rating system was devised by the U.S. Green Building Council (USGBC) to evaluate the environmental performance of a building and encourage market transformation toward sustainable design. There are several LEED rating systems for various project types including LEED for New Construction, LEED for Schools, LEED for Commercial Interiors and LEED for Homes.

Reason concrete can be used to build green include:

1.Concrete creates sustainable sites
2.Concrete enhances energy performance
3.Concrete contains recycled materials
4.Concrete is typically manufactured locally
5.Concrete builds durable structures

Following are just a few examples of how concrete can be used to increase the number of points awarded to building in the LEED system.

Brownfield Redevelopment (SS Credit 3)
Concrete can be used to solidify and stabilize contaminated soils and reduce leachate concentrations to below regulatory levels.

Site Development: Protect or Restore Habitat (SS Credit 5.1) & Maximize Open Space (SS Credit 5.2)
Concrete parking garages within buildings can limit site disturbance and restore previously developed sites. Parking garages within buildings help maintain natural areas that would otherwise be consumed by paved parking. This can contribute to SS Credit 5.1

Concrete parking garages can also help reduce the footprint of the development. Garages within buildings reduce the project's paved parking areas. This can contribute to SS Credit 5.2

Heat Island Effect: Nonroof (SS Credit 7.1)
This credit requires a combination of various strategies for 50% of the site hardscape (including roads, sidewalks, courtyards and parking lots) that will reduce heat islands or thermal gradient differences between developed and undeveloped areas. This can be met by using light colored concrete rather than asphalt for 50% of the impervious surfaces. This credit can also be met by placing a minimum of 50% of parking spaces under cover.

Optimize Energy Performance (EA Credit 1)
Studies show that using concrete walls that are insulated to exceed minimum code requirements by a modest amount can contribute to earning 1 to 3 points, depending on the building type, orientation and climate.

Low-Emitting Materials (IEQ Credit 4.2)
Credits can be earned by using low VOC products which may include products used specifically with concrete. This includes form releases, cures and sealers. Several US SPEC products in each of the above categories meet this requirement.

These are just a few examples of how building with concrete can support a project seeking LEED certification. For more information on the LEED program and project certification, please visit the USGBC web site, http://www.usgbc.org/.

Hot Weather Structural Grouting

Grout can be safely placed through the summer months in hot, dry climate's if certain precautions are taken. Hot weather is defined by the American Concrete Institute as, "a period when for more than 3 successive days the mean daily temperature is above 90 degrees. In order to apply grout in hot weather conditions, the following precautions must be followed:

1.Normal cement storage and handling practices should be observed. Store material should be observed. Store material indoors or in the shade with the plastic shrink-wrap removed. Use water cooled with ice, if needed. A fine screen can be used to filter out the ice when pouring the mix water.

2.Prior to grouting, it is crucial to keep the grout base saturated with water (SSD) for 24 hours in advance. The metal base plate should be cooled, and this can be accomplished with wet burlap or towels. If possible, create shade for the area to be grouted.

3.Begin grouting during the early part of the day to take advantage of the cooler temperatures.

4.During pumping applications, keep the pumping lines cool, especially with long lines. This can be accomplished with wet towels or rags. Use as little line as possible. Also, prior to priming the pump with cement slurry, pumping cold water through the lines will cool the lines down.

5.Mixing water shall be kept at a temperature of 30 degrees-50 degrees.

6.Hot weather will reduce the working time with the grout and smaller batches may be required. The compressive strength of the grout may be tested according to ASTM C-109. Use a surface thermometer to monitor temperature conditions of the grout.

US SPEC Non-shrink Grouts are formulated to meet the requirements of ASTM C-1107, CRD C-621 Corps of Engineers, and various DOT Specifications. US SPEC grouts include:

FS Grouting Special- Fast-setting, non-shrink precision grout
GP Grout-High strength, all purpose construction grout, plastic to fluid
MP Grout- High flow, high strength precision grout, damp pack to fluid
NA Grout-Aggregate free, super high flow, tendon grout
Premium Grout-High performance, high strength, high flow precision grout